Active matrix display device

ABSTRACT

A display device includes a dynamic ratioless shift register which is operated in a stable manner and can expand the degree of freedom of design. In the dynamic ratioless shift register which is provided with thin film transistors having semiconductor layers made of p-Si on a substrate surface, a node which becomes the floating state is connected to a fixed potential through a capacitance element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of application Ser. No.11/797,033, filed Apr. 30, 2007, now U.S. Pat. No. 7,397,472 which, inturn, is a continuation application of Ser. No. 10/857,944, filed Jun.2, 2004 (now U.S. Pat. No. 7,274,362), and, which, in turn, is acontinuation application of application Ser. No. 09/981,804, filed Oct.19, 2001 (now U.S. Pat. No. 6,801,194), the entire applicationdisclosures of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a display device, and, moreparticularly, to an active matrix type display device thereof.

In an active matrix type liquid crystal display device, pixel regionsare formed on a liquid crystal side surface of one of a pair ofsubstrates, which are arranged so as to face each other in an opposedmanner, with a liquid crystal being disposed therebetween. The pixelsare formed as regions which are surrounded by gate signal lines thatextend in the x direction and are arranged in parallel in the ydirection and drain signal lines that extend in the y direction and arearranged in parallel in the x direction.

Each pixel region is provided with a thin film transistor, which isoperated upon receiving a scanning signal from one gate signal line, anda pixel electrode to which video signals from the drain signal line aresupplied through the thin film transistor.

This pixel electrode generates an electric field between the pixelelectrode and a counter electrode which is formed on the other substrateside, for example, and the light transmittivity of the liquid crystaldisposed between these electrodes is controlled by this electric field.

Such a liquid crystal display device is provided with a scanning signaldriving circuit, which supplies scanning signals to respective gatesignal lines and a video signal line driving circuit which suppliesvideo signals to respective drain signal lines.

In view of the fact that the scanning signal driving circuit and thevideo signal line driving circuit are constituted of a large number ofMIS transistors having a constitution similar to that of the thin filmtransistors formed inside of the pixel regions, a technique has beenemployed in which semiconductor layers of these respective transistorsare formed of polycrystalline silicon (p-Si), and the scanning signaldriving circuit and the video signal line driving circuit are formed ona surface of one substrate along with the formation of the pixels.

The scanning signal driving circuit is a circuit which mainly uses ashift register, and the video signal line driving circuit also uses ashift register at a portion thereof. However, there has been a recentdemand for a shift register which can be operated at high speed at a lowvoltage and with a low power and which has no through-current. To meetthis demand, a shift register which is referred to as dynamic ratioshift register has been proposed, for example.

A dynamic ratio shift register of the type mentioned above has beendisclosed in Japanese Patent Publication No. 45638/1987, for example,and the constitution thereof is illustrated in FIG. 9A. Further, FIG. 9Bshows a timing chart of the circuit shown in FIG. 9A, which timing chartshows respective outputs VN1 and VN6 at nodes N1 and N6 corresponding toan input pulse φIN and synchronous pulses φ1, φ2.

First of all, when the synchronous pulse φ1 is changed from a Low level(referred to as “L” hereinafter) to a High level (referred to as “H”hereinafter) at the time t1, the input pulse φIN becomes “H”, and,hence, the potential VN1 of the node N1 is changed from “L” to “H”through a transistor NMT1.

Assuming the “L” state of the input pulse φIN and the synchronous pulsesφ1, φ2 having inverse phases from each other as a ground level (GND),and the “H” state of the input pulse φIN and the synchronous pulses φ1,φ2 as a threshold value Vth of Vφ<NMT1, the potential VN1 at this pointof time can be substantially expressed by the following equation (1).Here, Vφindicates the voltage at the “H” level of the synchronous pulsesφ1, φ2 and NMT1 indicates a MOS transistor.VN1=Vφ−Vth  (1)

Even when the synchronous pulse φ1 falls from “H” to “L” at the time t2,the input pulse φIN remains at the “H” level, and, hence, the output VN1holds the voltage expressed by the equation (1). In a strict sense, at apoint of time at which the synchronous pulse φ1 falls, the potentialbecomes lower than the voltage expressed by the equation (1) due to acapacitive coupling between a gate of the transistor NMT1 and the nodeN1 or the like. However, such a phenomenon is not essential in theexplanation of the operation, and, hence, the phenomenon is ignored.Since the transistor NMT1 turns OFF, the node N1 becomes a floatingnode.

Subsequently, when the synchronous pulse φ2 is changed from “L” to “H”at the time t2, provided that the following equation (2) is satisfied,Vφ−Vth≧Vφ  (2)The MOS transistor NMT2 turns ON and the pulse φ2 enters the node N2. Atthis point of time, due to the coupled capacitance CbI, which isreferred to as a bootstrap capacitance that is inserted between thenodes N1 and N2, a voltage rise on a point of the node N2 is transmittedto the node N1 which is in the floating state, so that the potential ofthe node N2 also rises.

Assuming that the rising potential of the node N2 is ΔVN2, the outputVN1 is given by a following equation (3):VN1=(Vφ−Vth)+ΔVN2(Cb/Cb(Cb+Cs))  (3)

Here, the capacitance Cb includes, besides the capacitance shown in thecircuit diagram, such as the preceding coupled capacitance CB1, all ofthe coupled capacitance of synchronous pulse φ2 and the node N1, whichinclude the capacitance generated' by the gate, the drain and the sourceof the transistor NMT2, or an inversion layer (channel) formed below thegate, and further include the direct connection capacitance between thewiring of the synchronous pulse φ2 and the node N1. Further, Csindicates a capacitance obtained by subtracting the above-mentionedbootstrap capacitance Cb from the whole capacitance of the node N1 andconstitutes the so-called parasitic capacitance.

Here, provided that the following equation (φ is satisfied at ΔVN2

Vφ.(Vφ−Vth)+Vφ(Cb/Cb(Cb+Cs))>Vφ+Vth  (4)This implies that the gate voltage of the MOS transistor NMT2, that is,the output VN1, becomes higher than Vφ+Vth. Accordingly, the output VN2can be set to the potential of the voltage Vφ. By suitably selecting thecapacitance Cb1, which constitutes a design element, it is easy tosatisfy the above-mentioned equation (4), and, hence, the output VN2 canbe set to the potential of the voltage Vφ.

Here, at the same time, the potential of the node N3 takes a valueexpressed by a following equation (5) through a MOS transistor NMT3,which is subjected to the diode connection.VN3=VφVth  (5)Since the MOS transistor NMT3 is subjected to diode connection, evenwhen the synchronous pulse φ2 is changed from “H” to “L” at the time t3,the state expressed by the above equation (5) can be held.

When the synchronous pulse φ1 is changed from “L” to “H” at the time t3,an operation similar to that expressed by the equation (3) occurs at thenode N3 and the MOS transistor NMT 5, so that the outputs VN3, VN4respectively generate the change of potential as schematically shown inFIG. 1B.

Here, when the nodes N2, N4, N6 are used as output nodes, shift pulses(VN2, VN4, VN6) having a potential equal to that of the “H” level of thesynchronous pulse can be obtained, and a dynamic operation which doesnot generate a through-current can be performed, as apparent from theabove-mentioned operations.

However, when the dynamic ratio register having such a constitution isformed by directly providing MIS transistors having semiconductor layerswhich are made of polycrystalline silicon (p-Si) to surfaces ofsubstrates (glass substrates) which are arranged to face each other inan opposed manner through a liquid crystal, it has been confirmed thatthe dynamic ratio register operates in an extremely unstable manner, sothat a countermeasure to cope with such a phenomenon is needed.

That is, the capacitance, when the floating nodes, such as N1, N3, areat the “L” level, is extremely small, and the other capacitance of thenodes N1, N2, including Cdg1, Cdg2, is, as shown at Cdg1, Cdg2 of FIG.9A, extremely small compared to the coupled capacitance between thesynchronous pulse and the drain gates of the nodes N1, N3. Hence, thereexists a high possibility that unselected transistors also will beturned “ON”. When the circuit remains as it is, the design and theoperational voltage are considerably restricted for holding the “OFF”state.

With respect to a monocrystalline semiconductor at the dynamic ratiolessshift register which are made of thin film transistors formed on theglass substrate, the main reasons why the capacitance becomes very smallwhen the floating node is at the “L” level are as follows.

FIG. 10A is a cross-sectional schematic view of an n-type MOS transistorformed on a monocrystalline semiconductor. A semiconductor integratedcircuit having a substrate which constitutes the semiconductor isgenerally used in a form in which it is biased (including the case thatit is grounded) for element separation or the like.

Accordingly, as shown in FIG. 10A, through a depletion layer capacitanceCsw due to an inverse bias between a source (a diffusion layer) and awell (or a substrate), a depletion layer capacitance Cdw between a drainand the well and a capacitance Cgw between a gate and the well, thesource, the drain and the gate are capacitively coupled with the well.Further, the wiring is also capacitively coupled with the substrate orthe well which is disposed immediately below the winding with thecapacitance Clw through a thick insulation film. These capacitancebelong to a group of capacitances which are usually called parasiticcapacitances.

Accordingly, at a portion of the node N3 shown in FIG. 9A, a largecoupling capacitance with the well can be obtained due to thecapacitance Csw of the NMT3 (Csw3), the capacitance Cgw of the NMT6(Cgw6), the capacitance Cdw (Cdw6), the capacitance Csw of the NMT7(Csw7) and the capacitance Clw (Clw3) of the wiring which constitutesthis node.

Further, by making the bootstrap capacitance have the enhanced MOScapacitive constitution which is shown in FIG. 10B and FIG. 10C, thewell is capacitively coupled with an inversion layer that extends from adepletion layer which constitutes a separate node at the “ON” time, asshown in FIG. 10B so that an efficient bootstrap effect (a boostingeffect) is obtained, while a coupled capacitance Cb1(w) with the well isobtained at the “OFF” time, as shown in FIG. 10B.

Accordingly, when the node N3 is at the “L” level, even when the node N3is floating on the circuit shown in FIG. 9A, the large capacitance canbe ensured with the bias of the well through the above-mentioned coupledcapacitance. With respect to the capacitance, the sum of Cdw of the NMT3(Cdw1) and the space capacitance C1 φ1 between the wiring of φ1 and thenode N3 is sufficiently small, and, hence, the potential difference ΔVN3of the node N3 when the wiring φ1 is changed from “L” to “H” issubstantially expressed by the following equation (6).ΔVN3=Vφ×(Cdw+C1φ1)/(Cdw1|C1φ2+Csw3+Cgw6+Cdw6+Csw7+Cb1(w))  (6)

Further, as explained above, since the relationship expressed by thefollowing equation (7) is established,Cdw1+C1φ2<<Csw3+Cgw6+Cdw6+Csw1+Cb1(w)  (7)it becomes easy to satisfy the following equation (8).ΔVN3<Vth  (8)However, when a similar circuit made of monocrystalline thin filmtransistors is formed on a glass substrate, the above-mentionedoperation is not achieved.

FIG. 10D is a cross-sectional schematic view of the monocrystalline thinfilm transistor which is formed on the glass substrate. Provided thatthe substrate is formed of an insulating body, once a p layer arrangedbelow a source, a drain or a gate becomes floating, the capacitancewhich can be coupled becomes the depletion layer capacitance Cdp, Cspbetween the source, or drain or the gate and the p layer arranged belowthe source, the drain or the gate or the small space capacitance Cs1,Cp1, Cd1 between the p layer and the wiring which is disposed so as tobe remote from the source, drain or the gate. To take a portion of thenode N3 of the circuit shown in FIG. 9A as an example, in the samemanner as the above-mentioned example, the node N3 is capacitivelycoupled with the node N2 through the source Csp3 of the MOS transistorNMT3. Since the node N2 is also floating, the path is divided into apath which brings about the capacitive coupling with the node N1 throughthe capacitance Cb1 and a path which brings about the capacitivecoupling with the synchronous pulse φ2 through the SP2 of the MOStransistor NMT2. Since the node N1 is also floating, the path is dividedinto a path which brings about the capacitive coupling with the inputpulse φIN through the capacitance Csp1 of the MOS transistor NMT1 and apath which brings about the capacitive coupling with the groundpotential Vss through the capacitance Csp4 of the MOS transistor NMT4,which brings about the capacitive coupling with the synchronous pulse φ1through the capacitance Csg1 of the MOS transistor NMT1.

That is, both capacitances also become very small and the coupling withthe synchronous pulse φ1 functions in such a manner that the output VN3is boosted when the synchronous pulse φ1 becomes “L”

“H”.

Although the source of a MOS transistor NMT7 is capacitively coupledwith the ground potential VSS through the capacitance Csp7, this is alsonot significant. Further, the node N3 is capacitively coupled with thenode N4 through the capacitance Cb2 so that the node N4 is alsofloating. The wiring which constitutes the node N3 does not have thecapacitance immediately below the node N3, and the node N3 has only aweak capacitive coupling with any one of the wirings through the spacecapacitance.

The node N3 is capacitively coupled with the synchronous pulse φ1through the capacitance Cdg5 of the MOS transistor NMT5. This capacitivecoupling is the direct capacitive coupling with the outside and isrelatively large. This capacitance becomes a cause of instability.

Assuming the total sum of the above-mentioned other secondary coupledcapacitance of the node N3, except for the capacitance Cdg5 as thecapacitance CN3, the change of potential AWN3 of the node N3 when thesynchronous pulse φ1 is changed from “L”

“H” is substantially expressed by a following equation (9). Since thecapacitance CN3 is not so large as mentioned above, depending on valuesof the voltage Vφ and the capacitance Cdg5 (W size design of the MOStransistor NMT5 or the wiring layout of the synchronous pulse φ1),conditions shown by the following equation (10) are easily broughtabout.ΔVN3=Vφ×(Cdg5/(Cdg5+CN3))  (9)ΔVN3≧Vth  (10)

Once the conditions indicated by the above equation (10) are satisfied,the capacitance Cgp of the MOS transistor NMT5 (the capacitance with theinversion layer) and the bootstrap capacitance Cb2 are changed to thecoupled capacitance with the node N3 and the φ1 in an opposed manner, sothat the possibility that the MOS transistor NMT3 turns completely “ON”due to the bootstrap effect is extremely increased. That is, an unstableoperation is generated such that nodes which are irrelevant to the nodeunder control become “H” and generate outputs or start the scanning fromsuch portions.

The present invention has been made in view of such a circumstance, andit is an object of the present invention to provide a display devicehaving a dynamic ratioless shift register which ensures stable operationand which can increase the degree of freedom of design.

SUMMARY OF THE INVENTION

A summary of typical features and aspects of the invention disclosed inthe present application are as follows.

Aspect 1.

The display device according to the present invention is, for example,characterized in that the display device is provided with a drivingcircuit which includes a shift register on a surface of a substrate, andthe shift register is constituted of MISTFTs which use polycrystallinesilicon as a semiconductor layer. The first terminal of the first MISTFTis connected to receive an input pulse, and a gate terminal of the firstMISTFT is connected to receive a first synchronous pulse, thus formingan inputting part. The second terminal of the first MISTFT is connectedto a gate terminal of the second MISTFT and the first terminal of thefourth MISTFT, and, further, it is connected to the first terminal ofthe first capacitance element. The second terminal of the firstcapacitance is connected to a fixed voltage and the first terminal ofthe second MISTFT is connected to receive a second synchronous pulsewhich has an inverse phase with respect to the first synchronous pulse.The second terminal of the second MISTFT is connected to the firstterminal and a gate terminal of the third MISTFT, and it is furtherconnected to the first terminal of the second capacitance. The secondterminal of the second capacitance is connected to the second terminalof the first MISTFT, the gate terminal of the second MISTFT and thefirst terminal of the fourth MISTFT. The second terminal of the thirdMISTFT is connected to a gate terminal of the fifth MISTFT and the firstterminal of the seventh MISTFT, and it is further connected to the firstterminal of the third capacitance element, thus forming a first outputterminal. The second terminal of the third capacitance is connected toreceive a fixed voltage and the first terminal of the fifth MISTFT isconnected to the first synchronous pulse. The second terminal of thefifth MISTFT is connected to the first terminal and a gate terminal ofthe sixth MISTFT and a gate terminal of the fourth MISTFT, and it isfurther connected to the first terminal of the fourth capacitance toform a second output terminal. The second terminal of the fourthcapacitance is connected to the second terminal of the third MISTFT, thegate terminal of the fifth MISTFT and the first terminal of the seventhMISTFT. The second terminal of the fourth MISTFT and the second terminalof the seventh MISTFT are connected to a fixed power source or a groundpotential which is equal to the voltage which will be the source voltageof the MISTFT which is included among the voltages of the first andsecond synchronous pulses, or which will be the source voltage of firstand second synchronous pulses which is not less than the thresholdvoltage of the fourth MISTFT, wherein a pulse which is shifted by oneclock and corresponds to a pulse inputted to the gate terminal of thefourth MISTFT is inputted to the gate terminal of the seventh MISTFT.

In the display device having such a constitution as describe above, oneside of the load capacitance is connected to a node which can befloating and the other side of the load capacitance is connected to thefixed potential or the like. Accordingly, the design tolerance in astate in which the above-mentioned unstable elements are eliminated canbe broadened so that a stable dynamic ratioless shift register includingthin film transistors made of polycrystalline silicon can be realized.

Aspect 2.

The display device according to the present invention is characterizedin that, for example, on the premise of the constitution of the aspect1, n basic circuits, each of which is constituted of the second toseventh MISTFTs and first to fourth capacitances are connected inmulti-stages. The gate terminal of the MISTFT which corresponds to thesecond MISTFT of the ith basic circuit is connected to the secondterminal of the MISTFT corresponding to the sixth MISTFT of the (i−1)thbasic circuit. The gate terminal of the MISTFT which corresponds to theseventh MISTFT of the ith basic circuit is connected to the secondterminal of the MISTFT corresponding to the second MISTFT of the (i+1)thbasic circuit. The pulse which corresponds to the pulse inputted to thegate terminal of the fourth MISTFT of the basic circuit of a next stageand is shifted by one clock is inputted to the gate terminal of theMISTFT which corresponds to the seventh MISTFT of the nth basic circuit.

Aspect 3.

The display device according to the present invention is characterizedin that, for example, on the premise of the constitution of the aspect2, the second MISTFT is incorporated into the first basic circuit, andthe first MISTFT and the second MISTFT are incorporated into each one ofthe second and succeeding basic circuits. The first MISTFT has the gateterminal thereof connected to the input terminal for receipt of theinput pulse, the first terminal thereof connected to the gate terminalof the MISTFT corresponding to the second MISTFT, and the secondterminal thereof connected to a fixed power source or a ground potentialwhich is equal to the voltage which will be the source voltage of theMISTFT, which is included among the voltages of the first and secondsynchronous pulses, or which will be the source voltage of first andsecond synchronous pulses, which is not less than the threshold voltageof the fourth MISTFT. The second MISTFT has the gate terminal thereofconnected to the input terminal of the input pulse, the first terminalthereof connected to the gate terminal the fifth MISTFT or the gateterminal of a MISTFT corresponding to the fifth MISTFT, and the secondterminal thereof connected to a fixed power source or a groundpotential, which is equal to a voltage which becomes a source voltage ofthe MISTFT out of the voltages of the first and second synchronouspulses, or which is not different from the voltage which becomes thesource voltage of the first or second synchronous pulse to an extentthat the fixed power source or the ground potential at least does notexceed a threshold value voltage of the fourth MISTFT.

Aspect 4.

The display device according to the present invention is, for example,characterized in that the display device is provided with a drivingcircuit which includes a shift register on a surface of a substrate, andthe shift register is constituted of MISTFTs which use polycrystallinesilicon as a semiconductor layer. The first terminal and a gate terminalof the first MISTFT are connected to receive an input pulse, thusforming an inputting part. The second terminal of the first MISTFT isconnected to a gate terminal of the second MISTFT and the first terminalof the fourth MISTFT, and, further, it is connected to a first terminalof a first capacitance element. The second terminal of the firstcapacitance element is connected to a fixed voltage and the firstterminal of the second MISTFT is connected to receive a secondsynchronous pulse which has an inverse phase with respect to the firstsynchronous pulse. The second terminal of the second MISTFT is connectedto the first terminal and a gate terminal of the third MISTFT, and is itfurther connected to a first terminal of a second capacitance. Thesecond terminal of the second capacitance is connected to the secondterminal of the first MISTFT, the gate terminal of the second MISTFT andthe first terminal of the fourth MISTFT. The second terminal of thethird MISTFT is connected to a gate terminal of the fifth MISTFT and thefirst terminal of the seventh MISTFT, and it is further connected to thefirst terminal of the third capacitance element, thus forming a firstoutput terminal. The second terminal of the third capacitance isconnected to a fixed voltage and the first terminal of the fifth MISTFTis connected to the first synchronous pulse. The second terminal of thefifth MISTFT is connected to the first terminal and a gate terminal ofthe sixth MISTFT and a gate terminal of the fourth MISTFT, and it isfurther connected to the first terminal of the fourth capacitance toform the second output terminal. The second terminal of the fourthcapacitance is connected to the second terminal of the third MISTFT, thegate terminal of the fifth MISTFT and the first terminal of the seventhMISTFT. The second terminal of the fourth MISTFT and the second terminalof the seventh MISTFT are connected to a fixed power source or a groundpotential, which is equal to the voltage which will be the sourcevoltage of the MISTFT, which is included among the voltages of the firstand second synchronous pulses, or which will be the source voltage offirst and second synchronous pulses which is not less than the thresholdvoltage of the fourth MISTFT, wherein a pulse which is shifted by oneclock and corresponds to a pulse inputted to the gate terminal of thefourth MISTFT is inputted to the gate terminal of the seventh MISTFT.

Aspect 5.

The display device according to the present invention is characterizedin that, for example, on the premise of the constitution of the aspect4, n basic circuits, each of which is constituted of the second toseventh MISTFT5 and first to fourth capacitance, are connected inmulti-stages. The gate terminal of the MISTFT, which corresponds to thesecond MISTFT of the ith basic circuit, is connected to the secondterminal of the MISTFT corresponding to the sixth MISTFT of the (i−1)thbasic circuit. The gate terminal of the MISTFT, which corresponds to theseventh MISTFT of the ith basic circuit, is connected to the secondterminal of the MISTFT corresponding to the second MISTFT of the (i+1)thbasic circuit. The pulse which corresponds to the pulse inputted to thegate terminal of the fourth MISTFT of the basic circuit of a next stageand is shifted by one clock is inputted to the gate terminal of theMISTFT which corresponds to the seventh MISTFT of the nth basic circuit.

Aspect 6.

The display device according to the present invention is characterizedin that, for example, on the premise of the aspect 5, the second MISTFTis incorporated into the first basic circuit, and the first MISTFT andthe second MISTFT are incorporated into each one of the second andsucceeding basic circuits. The first MISTFT has the gate terminalthereof connected to the input terminal of the input pulse, the firstterminal thereof connected to the gate terminal of the MISTFTcorresponding to the second MISTFT, and the second terminal thereofconnected to a fixed power source or a ground potential which is equalto the voltage which will be the source voltage of the MISTFT, which isincluded among the voltages of the first and second synchronous pulses,or which will be the source voltage of first and second synchronouspulses which is not less than the threshold voltage of the fourthMISTFT. The second MISTFT has the gate terminal thereof connected to theinput terminal of the input pulse, the first terminal thereof connectedto the gate terminal of the fifth MISTFT or the gate terminal of aMISTFT corresponding to the fifth MISTFT, and the second terminalthereof connected to a fixed power source or a ground potential which isequal to the voltage which will be the source voltage of the MISTFT,which is included among the voltages of the first and second synchronouspulses, or which will be the source voltage of first and secondsynchronous pulses which is not less than the threshold voltage of thefourth MISTFT.

Aspect 7.

The display device according to the present invention is, for example,characterized in that the display device is provided with a drivingcircuit which includes a shift register on a surface of a substrate, andthe shift register is constituted of MISTFTs which use polycrystallinesilicon as a semiconductor layer. The first terminal and a gate terminalof the first MISTFT are connected to an input pulse thus forming aninputting part. The second terminal of the first MISTFT is connected toa gate terminal of the second MISTFT and the first terminal of thefourth MISTFT, and, further, it is connected to a fixed voltage throughthe first capacitance. The first terminal of the second MISTFT isconnected to the second synchronous pulse which has an inverse phasewith respect to the first synchronous pulse. The second terminal of thesecond MISTFT is connected to the first terminal and a gate terminal ofthe third MISTFT, and it is further connected to the second terminal ofthe first MISTFT, the gate terminal of the second MISTFT and the firstterminal of the fourth MISTFT. The second terminal of the third MISTFTis connected to a gate terminal of the fifth MISTFT and the firstterminal of the seventh MISTFT, and it is further connected to the fixedvoltage through the third capacitance element. The first terminal of thefifth MISTFT is connected to the first synchronous pulse. The firstterminal of the fifth MISTFT is connected to the first terminal and agate terminal of the sixth MISTFT and a gate terminal of the fourthMISTFT, and it is further connected to the second terminal of thirdMISTFT, the gate terminal of the fifth MISTFT and the first terminal ofthe seventh MISTFT through the fourth capacitance element. The secondterminal of the fourth MISTFT is connected to a fixed power source or aground potential, which is equal to the voltage which will be the sourcevoltage of the MISTFT, which is included among the voltages of the firstand second synchronous pulses, or which will be the source voltage offirst and second synchronous pulses which is not less than the thresholdvoltage of the fourth MISTFT. wherein a pulse which is shifted by oneclock and corresponds to a pulse inputted to the gate terminal of thefourth MISTFT is inputted to the gate terminal of the seventh MISTFT.

Aspect 8.

The display device according to the present invention is characterizedin that, for example, on the premise of the constitution of the aspect7, n basic circuits, each of which is constituted of the second toeleventh MISTFT5 and the first and second capacitances are connected inmulti-stages. The gate terminal of the MISTFT, which corresponds to thesecond MISTFT of the ith basic circuit, is connected to the secondterminal of the MISTFT corresponding to the tenth MISTFT of the (i−i)thbasic circuit. The gate terminal of the MISTFT which corresponds to theeighth MISTFT and the first terminal of the MISTFT which corresponds tothe seventh MISTFT of the ith basic circuit are connected to the secondterminal of the MISTFT corresponding to the sixth MISTFT of the (i+i)thbasic circuit. The pulse which corresponds to the pulse inputted to thegate terminal of the fourth MISTFT and is shifted by one clock isinputted to the gate terminal of the MISTFT which corresponds to theeighth MISTFT and the first terminal of the MISTFT which corresponds tothe seventh MISTFT of the nth basic circuit.

Aspect 9.

The display device according to the present invention is, for example,characterized in that the display device is provided with a drivingcircuit which includes a shift register on a surface of a substrate, andthe shift register is constituted of MISTFTS which use polycrystalliflesilicon as a semiconductor layer. The first terminal of the first MISTFTis connected to an input pulse, and a gate terminal of the first MISTFTis connected to the first synchronous pulse, thus forming an inputtingpart. The second terminal of the first MISTFT is connected to a gateterminal of the fourth MISTFT and the first terminal of the thirdMISTFT, and, further, it is connected to the first terminal of the firstcapacitance. The second terminal of the first capacitance is connectedto the second terminal of the fourth MISTFT, the first terminal and agate terminal of the fifth MISTFT and the first terminal and a gateterminal of the sixth MISTFT, and it is further connected to a gateterminal of the seventh MISTFT, a gate terminal of the second MISTFT isconnected to the input pulse, and the first terminal of the secondMISTFT is connected to the second terminal of the eleventh MISTFT and agate terminal of the third MISTFT. The second terminal of the secondMISTFT and the second terminal of the seventh MISTFT are connected to afixed power source or a ground potential, which is equal to the voltagewhich will be the source voltage of the MISTFT, which is included amongthe voltages of the first and second synchronous pulses, or which willbe the source voltage of first and second synchronous pulses which isnot less than the threshold voltage of the fourth MISTFT. The secondterminal of the third MISTFT is connected to a fixed power source or aground potential, which is equal to the voltage which will be the sourcevoltage of the MISTFT, which is included among the voltages of the firstand second synchronous pulses, or which will be the source voltage offirst and second synchronous pulses which is not less than the thresholdvoltage of the fourth MISTFT. The first terminal of the fourth MISTFT isconnected to the second synchronous pulse, and the second terminal ofthe fifth MISTFT is connected to a gate terminal of the ninth MISTFT andthe first terminal of the eighth MISTFT. The second terminal of thesecond capacitance is connected to the second terminal of the ninthMISTFT, the first terminal and a gate terminal of the tenth MISTFT andthe first terminal and a gate terminal of the eleventh MISTFT, and,further it is connected to the first terminal of the second capacitanceelement, thus forming the first output terminal. The first terminal ofthe seventh MISTFT is connected to the gate terminal of the eighthMISTFT, and the second terminal of the eighth MISTFT is connected to afixed power source or a ground potential, which is equal to the voltagewhich will be the source voltage of the MISTFT, which is included amongthe voltages of the first and second synchronous pulses, or which willbe the source voltage of first and second synchronous pulses which isnot less than the threshold voltage of the fourth MISTFT. The firstterminal of the ninth MISTFT is connected to the first synchronouspulse, wherein a pulse which is shifted by one clock and corresponds toa pulse inputted to the gate terminal of the fourth MISTFT is inputtedto the gate terminal of the eighth MISTFT and the first terminal of theseventh MISTFT.

Aspect 10.

The display device according to the present invention is characterizedthat, for example, on the premise of the constitution of the aspect 9, nbasic circuits, each of which is constituted of the second, third,fourth, fifth, seventh, eighth, ninth and tenth MISTFTS and the firstand second capacitance, are connected in multi-stages. The secondterminal of a MISTFT which corresponds to the tenth MISTFT of the ithbasic circuit is connected to the gate terminal of the MISTFTcorresponding to the fourth MISTFT of the (i−i)th basic circuit. Thesecond terminal of the MISTFT which corresponds to the seventh MISTFTand the gate terminal of the MISTFT which corresponds to the thirdMISTFT of the ith basic circuit are connected to the capacitancecorresponding to the first capacitance of the (i+i)th basic circuitthrough the sixth MISTFT. The second terminal of the sixth MISTFT isconnected to the second terminal of the MISTFT and the gate terminal ofthe MISTFT which corresponds to the third MISTFT and the first terminaland the gate terminal of the sixth MISTFT is connected to thecapacitance.

Aspect 11.

The display device according to the present invention is characterizedin that, for example, at respective basic circuits starting from asecond basic circuit, the second terminal of first MISTFT, which has thefirst terminal thereof and a gate terminal thereof connected to an inputpulse, is connected to the second terminal of a MISTFT which correspondsto an eleventh MISTFT. At respective basic circuits starting from athird basic circuit, the second terminal of the second MISTFT, which hasthe first terminal thereof and a gate terminal thereof connected to aninput pulse, is connected to a gate terminal of a MISTFT whichcorresponds to the eighth MISTFT of the basic circuit, which forms apre-stage of the subject basic circuit, and is connected to the secondterminal of capacitance which corresponds to the first capacitancethrough the MISTFT. The second terminal of the MISTFT is connected tothe second terminal of the second MISTFT, and the first terminal and thegate terminal are connected to the capacitance.

Aspect 12.

The display device according to the present invention is, for example,characterized in that the display device is provided with a drivingcircuit which includes a shift register on a surface of a substrate, andthe shift register is constituted of MISTFTs which use polycrystallinesilicon as a semiconductor layer. The first terminal and a gate terminalof the first MISTFT are connected to receive an input pulse, thusforming an input part. The second terminal of the first MISTFT isconnected to a gate terminal of the fourth MISTFT and the first terminalof the third MISTFT, and, further it is connected to the first terminalof the first capacitance. The second terminal of the first capacitanceis connected to the second terminal of the fourth MISTFT, the firstterminal and a gate terminal of the fifth MISTFT and the first terminaland a gate terminal of the sixth MISTFT, and it is further connected toa gate terminal of the seventh MISTFT. A gate terminal of the secondMISTFT is connected to the input pulse, and the first terminal of thesecond MISTFT is connected to the second terminal of the eleventh MISTFTand a gate terminal of the third MISTFT. The second terminal of thesecond MISTFT and the second terminal of the seventh MISTFT areconnected to a fixed power source or a ground potential, which is equalto the voltage which will be the source voltage of the MISTFT, which isincluded among the voltages of the first and second synchronous pulses,or which will be the source voltage of first and second synchronouspulses which is not less than the threshold voltage of the fourthMISTFT. The second terminal of the third MISTFT is connected to a fixedpower source or a ground potential, which is equal to the voltage whichwill be the source voltage of the MISTFT, which is included among thevoltages of the first and second synchronous pulses, or which will bethe source voltage of first and second synchronous pulses which is notless than the threshold voltage of the fourth MISTFT.

The first terminal of the fourth MISTFT is connected to the secondsynchronous pulse, and the second terminal of the fifth MISTFT isconnected to a gate terminal of the ninth MISTFT and the first terminalof the eighth MISTFT. The second terminal of the second capacitance isconnected to the second terminal of the ninth MISTFT, the first terminaland a gate terminal of the tenth MISTFT and the first terminal and agate terminal of the eleventh MISTFT, and, further it is connected tothe first terminal of the second capacitance element thus, forming thefirst output terminal. The first terminal of the seventh MISTFT isconnected to the gate terminal of the eighth MISTFT, and the secondterminal of the eighth MISTFT is connected to a fixed power source or aground potential, which is equal to the voltage which will be the sourcevoltage of the MISTFT, which is included among the voltages of the firstand second synchronous pulses, or which will be the source voltage offirst and second synchronous pulses, which is not less than thethreshold voltage of the fourth .MISTFT. The first terminal of the ninthMISTFT is connected to the first synchronous pulse, wherein a pulsewhich is shifted by one clock and corresponds to a pulse inputted to thegate terminal of the fourth MISTFT is inputted to the gate terminal ofthe eighth MISTFT and the first terminal of the seventh MISTFT.

Aspect 13.

The display device according to the present invention is characterizedin that, for example, on the premise of the constitution of the aspect12, n basic circuits, each of which is constituted of the second, third,fourth, fifth, seventh, eighth, ninth and tenth MISTFTs and the firstand second capacitances are connected in multi-stages. The secondterminal of the MISTFT, which corresponds to the tenth MISTFT of the ithbasic circuit, is connected to the gate terminal of the MISTFTcorresponding to the fourth MISTFT of the (i−I)th basic circuit. Thesecond terminal of the MISTFT which corresponds to the seventh MISTFTand the gate terminal of the MISTFT which corresponds to the thirdMISTFT of the ith basic circuit are connected to the capacitancecorresponding to the first capacitance of the (i+1)th basic circuitthrough the sixth MISTFT. The second terminal of the sixth MISTFT isconnected to the second terminal of the MISTFT and the gate terminal ofthe MISTFT which corresponds to the third MISTFT and the first terminaland the gate terminal of the sixth MISTFT are connected to thecapacitance.

Aspect 14.

The display device according to the present invention is characterizedin that, on the premise of the aspect 13, at respective basic circuitsstarting from the second basic circuit, the second terminal of the firstMISTFT, which has the first terminal thereof and a gate terminal thereofconnected to an input pulse, is connected to the second terminal of aMISTFT which corresponds to the eleventh MISTFT. At respective basiccircuits starting from the third basic circuit, the second terminal ofthe second MISTFT, which has the first terminal thereof and a gateterminal thereof connected to an input pulse, is connected to a gateterminal of a MISTFT which corresponds to the eighth MISTFT of a basiccircuit, which forms a pre-stage of the subject basic circuit, and isconnected to the second terminal of capacitance which corresponds to thefirst capacitance through the MISTFT. The second terminal of the MISTFTis connected to the second terminal of the second MISTFT and the firstterminal and the gate terminal are connected to the capacitance.

Aspect 15.

The display device according to the present invention is, for example,provided with a ratioless dynamic shift' register which includesmulti-staged inverters on a substrate surface. The ratioless dynamicshift register is constituted of MISTFTs which use polycrystallinesilicon as a semiconductor layer. Separate MISTFTs are connected inparallel to MISTFTs which are connected to ground levels of outputs ofrespective stages, and the separate MISTFTs are constituted such thateach output is dropped to a ground level during a period other than aperiod in which a signal of High level is transmitted as an input signalof an inverter at a stage preceding to a stage which is constituted ofthe MISTFTs.

Aspect 16.

The display device according to the present invention is, on the premiseof the constitution of the aspect 15, characterized in that the separateMISTFTs are operated by inputting outputs of the next stage, and eachoutput is dropped to the ground level during the period other than theperiod in which the signal of High level is transmitted as the inputsignal of the inverter at the stage preceding to the stage which isconstituted of the MISTFT.

Aspect 17.

The display device according to the present invention is, for example,on the premise of the constitution of the Aspect 15, characterized inthat the separate MISTFT is operated by inputting a clock pulse, andeach output is dropped to the ground level during the period other thanthe period in which the signal of High level is transmitted as the inputsignal of the inverter at the stage preceding to the stage which isconstituted of the MISTFT.

Aspect 18.

The display device according to the present invention is, for example,characterized in that the display device is provided with a displaydriving circuit including a ratioless dynamic shift register which iscomprised of multi-staged inverters on a substrate surface. Theratioless dynamic shift register is constituted of MISTFTs which usepolycrystalline silicon as a semiconductor layer, and the first MISTFT,and the second MISTFT which are connected in parallel to each other, areprovided as MISTFTs which are connected to the ground levels ofrespective outputs of respective stages. Either one of the first MISTFTand the second MISTFT is constituted such that each output is dropped tothe ground level during the period other than the period in which thesignal of High level is transmitted as the input signal of the inverterat the stage preceding to the stage which is constituted of the MISTFT.A diode which constitutes the third MISTFT is provided between a gate ofeither one of the first MISTFT and the second MISTFT and a node to whicha clock is supplied through a diode, such that a charge which is chargedto the gate is prevented from leakage to the node as an inverse currentflow of the diode which is caused by the lowering of the potential ofthe node below the ground level.

Aspect 19.

The display device according to the present invention is, for example,characterized in that the display device is provided with a displaydriving circuit including a ratioless dynamic shift register which iscomprised of multi-staged inverters on a substrate surface. Theratioless dynamic shift register is constituted of MISTFT5 which usepolycrystalline silicon as a semiconductor layer, and a first MISTFT anda second MISTFT are provided, which drop respective outputs ofrespective stages to a ground level when the first clock and the secondclock are in the “ON” state and the third MISTFT and the fourth MISTFTwhich become the “ON” state when the outputs are at the “High” level andturn off the first MISTFT and the second MISTFT.

Aspect 20.

The display device according to the present invention is, for example,on the premise of the constitution of the Aspect 19, characterized inthat the first clock is inputted to the gate of the first MISTFT throughthe first capacitance element, the second clock is inputted to the gateof the second MISTFT through the second capacitance element, and thefifth MISTFT and the sixth MISTFT which are respectively subjected tothe diode connection are provided between the gate of the first MISTFTand the ground level and between the gate of the second MISTFT and theground level.

Aspect 21.

The display device according to the present invention is, for example,characterized in that the display device is provided with a displaydriving circuit including a ratioless dynamic shift register which iscomprised of multi-staged inverters on a substrate surface. Theratioless dynamic shift register is constituted of MISTFTS which usepolycrystalline silicon as a semiconductor layer. A first MISTFT isprovided, which is connected to ground levels of respective outputs ofrespective stages, and a second MISTFT is provided, which is operatedwith an output of a preceding stage and has one end thereof connected toa ground level and the other end thereof connected to a clock throughthe first capacitance element and further has the other end thereofconnected to a gate of the first MISTFT. A second capacitance element isdisposed between the other end of the second MISTFT and the groundlevel.

Aspect 22.

The display device according to the present invention is, for example,on the premise of the Aspect 21, characterized in that the secondcapacitance element has a capacitance larger than a gate-draincapacitance of the second MISTFT.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic circuit diagram and FIG. 1B is a timing chart ofone embodiment of a shift register formed on a substrate of a displaydevice according to the present invention.

FIG. 2 is a schematic diagram of one embodiment showing the overallconfiguration of the display device according to the present invention.

FIGS. 3A to 3C are diagrams showing the capacitance or the like which isgenerated by a thin film transistor which constitutes a shift registerformed on a substrate of display device according to the presentinvention.

FIG. 4 is a schematic circuit diagram showing another embodiment of ashift register formed on a substrate of a display device according tothe present invention.

FIG. 5 is a schematic circuit diagram showing another embodiment of ashift register formed on a substrate of a display device according tothe present invention.

FIG. 6A is a schematic circuit diagram and FIG. 6B is a timing chartshowing another embodiment of a shift register formed on a substrate ofa display device according to the present invention.

FIG. 7A is a schematic circuit diagram and FIG. 7B is a timing chartshowing another embodiment of a shift register formed on a substrate ofa display device according to the present invention.

FIG. 8 is a schematic circuit diagram showing another embodiment of ashift register formed on a substrate of a display device according tothe present invention.

FIG. 9A is a schematic circuit diagram and FIG. 9B is a timing chartshowing one example of a dynamic ratioless shift register formed on amonocrystalline semiconductor layer.

FIGS. 10A to 10F are diagrams which indicate the difference between acase in which the dynamic ratioless shift transistor is formed on aglass substrate and a case in which the dynamic ratioless shifttransistor is formed on a monocrystalline semiconductor layer.

FIG. 11 is a schematic circuit diagram showing another embodiment of thedynamic ratioless shift register used in the display device according tothe present invention.

FIG. 12 is an input pulse timing chart for the circuit shown in FIG. 11.

FIG. 13 is a schematic circuit diagram provided for comparison toclarify a characterizing portion of the circuit shown in FIG. 11.

FIG. 14 is an input pulse timing chart for the circuit shown in FIG. 11.

FIGS. 15A to 15E are waveform diagrams showing inconvenient points inexplaining the circuit shown in FIG. 13 and the circuit shown in FIG.11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of a display device according to a presentinvention will be explained in conjunction with accompanying drawings.

<<Overall Constitution>>

FIG. 2 is a schematic diagram showing the overall configuration of aliquid crystal display device according to the present invention. Thisdrawing constitutes a plan view which is drawn corresponding to anactual geometrical arrangement.

In the drawing, for example, a transparent substrate SUB1, which isformed of a glass substrate, constitutes one of a pair of transparentsubstrates that are arranged to face each other in an opposed mannerthrough a liquid crystal. On a central portion (display portion AR),excluding the periphery of the liquid-crystal-side surface of thetransparent substrate SUB1, gate signal lines GL, which extend in the xdirection and are arranged in the y direction in the drawing, and drainsignal lines DL, which extend in the y direction and are arranged in thex direction in the drawing, are formed.

Each region, which is surrounded by neighboring gate signal lines GL andthe neighboring drain signal lines DL, define a pixel region. The pixelregion is provided with a thin film transistor TFT, which is operatedupon receiving scanning signals from the gate signal line GL at one sideand a pixel electrode PX to which video signals are supplied from thedrain signal line DL at one side through the thin film transistor TFT.That is, scanning signals (voltages) are sequentially supplied to therespective gate signal lines GL from the top to the bottom in thedrawing, for example, and the thin film transistors TFT are turned ON inresponse to these scanning signals. In synchronism with this timing,video signals (voltages) are supplied from the respective drain signallines DL, and these video signals are applied to the pixel electrodes PXthrough those thin film transistors TFT that are in the ON state.

These respective pixel electrodes PX generate an electric field betweenthe pixel electrodes PX and a counter electrode (not shown in thedrawing) which is commonly formed at respective pixel regions on aliquid crystal side surface of other transparent substrate, which isarranged to face the transparent substrate SUB1 in an opposed manner,for example. The light transmittivity of the liquid crystal iscontrolled by this electric field.

The respective gate signal lines GL have one end thereof (left side inthe drawing) connected to a pixel driving shift register 1, and thescanning signals are sequentially supplied to respective gate signalslines GL by the pixel driving shift register 1. The respective drainsignal lines DL have one end (upper side in the drawing) connectedsequentially to a D-A conversion circuit 2. a memory 3, an input dataentry circuit 4 and an H-side address decoder 5, while a V-side addressdecoder 6 and a memory driving shift register 7 are connected to thememory 3.

To the liquid crystal display device having such a constitution,information including a start pulse clock signal, pixel data, a pixeladdress (H) and a pixel address (V) are inputted. The start pulse clocksignal is inputted to the memory driving shift register 7 and the pixeldriving shift register 1. The pixel address (H) is inputted to theH-side address decoder 5. The pixel data is inputted to the input dataentry circuit 4. The pixel address (V) is inputted to the V-side addressdecoder 6.

Here, at a display part AR, which is formed on a surface of thetransparent substrate SUB1, and at respective circuits arranged aroundthe display part AR, the thin film transistors (MISTFT) which are formedby laminating conductive layers, semiconductor layers, insulation layersand the like, and the pixel electrodes, the signal lines and the like,which are formed into a given pattern by an selective etching using aphotolithography technique, are provided.

In this case, the semiconductor layer is formed of polycrystallinesilicon (P-Si), for example.

<<Pixel Driving Shift Register>>

FIG. 1A is a circuit diagram showing one embodiment of the pixel drivingshift register. Further, FIG. 1B is a timing chart for the circuit shownin FIG. 1A, showing outputs VN1 to VN6 respectively corresponding tonodes N1 to N6 with respect to an input pulse φIN and synchronous pulsesφ1, φ2.

In FIG. 1A, first of all, an n-type MOS transistor NMT1 is provided. Ofthe source and drain terminals, one terminal is connected to an inputterminal (PIN of the input pulse φIN, and the gate terminal is connectedto an input terminal of the synchronous pulse φ1. This MOS transistorNNT1 constitutes an inputting part.

The other terminal of the MOS transistor NMT1 is connected to a gateterminal of an n-type MOS transistor NMT2, one terminal of an n-type MOStransistor NMT4 and one terminal of a capacitance element CS1. The otherterminal of the capacitance element CS1 is connected to a fixed voltageVBIAS, and one terminal of the MOS transistor NMT2 is connected to aninput terminal of the synchronous pulse φ2 which forms an inverse phasewith respect to the previously mentioned synchronous pulse φ1.

The other terminal of the MOS transistor NMT2 is connected to oneterminal of the n-type MOS transistor NMT3 and the gate terminal, and itis further connected to one terminal of the capacitance element Cb1. Theother terminal of the capacitance element Cb1 is connected to the otherterminal of the MOS transistor NMT1, the gate terminal of the MOStransistor NMT2 and one terminal of the n-type MOS transistor NNT4.

The other terminal of the MOS transistor NMT3 is connected to a gateterminal of an n-type MOS transistor NMT5 and one terminal of a MOStransistor NMT7. Further, the other terminal of the MOS transistor NMT3is connected to one terminal of the capacitance element CS2. The otherterminal of the MOS transistor NMT3 constitutes the first outputterminal. The other terminal of the capacitance element CS2 is connectedto a fixed voltage VBIAS, and one terminal of the MOS transistor NMT5 isconnected to an input terminal of the synchronous pulse φ1.

The other terminal of the MOS transistor NMT5 is connected to oneterminal and a gate terminal of an n-type MOS transistor NMT6 and a gateterminal of the MOS transistor NMT4. The other terminal of the MOStransistor NMT5 is further connected to one terminal of the capacitanceelement Cb2. The other terminal of the MOS transistor NMT5 constitutesthe second output terminal. The other terminal of the capacitanceelement Cb2 is connected to the other input terminal of the MOStransistor NMT3, the gate terminal of the MOS transistor NMT5 and oneterminal of the n-type MOS transistor NMT7.

The other terminal of the MOS transistor NMT4 and the other terminal ofthe MOS transistor NMT7 are connected to a fixed power source or aground potential (VSS/VDD) which is equal to a voltage, which becomes asource voltage of the MOS transistor out of the voltages of theabove-mentioned synchronous pulses φ1, φ2 (minimum voltage when thetransistor is of n-type and maximum voltage when the transistor is ofp-type), or which will be the source voltage of the first or the secondsynchronous pulse φ1, φ2 which is not less than the threshold voltagevalue of MOS transistor NMT4.

Such a connection is adopted in a next stage and succeeding stages in asimilar manner, wherein the gate terminal of the MOS transistor NMT7 isconnected to a gate terminal of a MOS transistor NMT9 corresponding tothe MOS transistor NMT4 in the next stage.

With respect to the shift register having such a constitution, as shownin FIG. 1A, one side of load capacitances CS1, CS2, CS3, . . . isrespectively connected to the nodes N1, N3, N5, . . . which can befloating, and the other side of these load capacitances CS1, CS2, CS3 .. . is connected to a fixed potential VBIAS. Due to such a constitution,the above-mentioned equation (9) can be rewritten as following equation(11).VN3=Vφ×(Cdg5/(Cdg5+CN3+CS2))  (11)Here, the capacitance CS2 constitutes a design parameter and, at thesame time, can be formed of a direct parallel plate capacitance. Evenwhen the capacitance CN3 is ignored, the output VN3 can be expressed bythe following equation (12).VN3=Vφ×(Cdg5/(Cdg5+CS2))<Vth  (12)Further, the following equation (13), which is formulated by adding thecapacitance CS (CS2 from node N3) to the previously mentioned equation(4), is satisfied.VN1=(Vφ−Vth)+Vφ(Cb/(Cb+CS+cs))>Vφ+Vth  (13)

From the above, the design tolerance, in the case in which theabove-mentioned unstable elements are eliminated can be expanded so thatthe stable dynamic ratioless shift register which includes thin filmtransistors formed of polycrystalline silicon can be realized.

FIG. 3A is a cross-sectional view of a thin film transistor whichconstitutes a circuit in which the above-mentioned dynamic ratiolessshift register is formed on the transparent substrate SUB1. In formingthe load capacitance CS in this thin film transistor, the capacitanceCs1 between the polysilicon thin film and the wiring material, thecapacitance CgI between the gate forming thin film and the wiringmaterial, the capacitance Ctg between the gate forming thin film and thepixel electrode, the capacitance Ct1 between the wiring material and thepixel electrode or the like can be designated a specific candidate.

In the above-mentioned constitution, the added load capacitance CSperforms an important role from the viewpoint of stable operation of thecircuit and can enhance the degree of freedom of design. However, theload capacitance CS totally constitutes a parasitic capacitance from theview point of a bootstrap efficiency.

Accordingly, the MOS capacitance shown in FIG. 3B and FIG. 3C are formedas the load capacitance CS, and the bootstrap efficiency can be enhancedwith such load capacitance CS. That is, assuming that the fixed voltageVBIAS is set as expressed in a following equation (14),Vth<VBIAS<Vφ−2Vth  (14)and the source side is connected to the floating node and the gate sideis connected to the bias, a variable capacitance, can be generated inwhich, when the floating node (N3, N5, . . . ) is “L”, an inversionlayer is formed so that the capacitance becomes large (CSL), while whenthe floating node (N3, N5, . . . ) is “H”, the inversion layer is notpresent, so that the capacitance becomes small. (CSS). That is, therelationship expressed by a following equation (15) can be obtained.CSL>>CSS  (15)

Accordingly, the above-mentioned equations (12) (13) are respectivelyrewritten as following equations (16), (17) so that the stabilizedcapacitance becomes heavy and the bootstrap efficiency can be enhanced.VN3=Vφ×(Cdgs/(CdgS+CSL))<Vth  (16)VN1=(Vφ−Vth)+(Cb/(Cb+CSS+Cs))>Vφ+Vth  (17)

FIG. 4 shows another embodiment which represents a further improvementover the circuit shown in FIG. 1.

In this embodiment, assuming a circuit which forms the first output of anext stage and a circuit which forms the second output in a subsequentstage in an inputting part as basic circuits, a MOS transistor NMTr2 isincorporated into the first-stage basic circuit and a MOS transistorNMTr1 and the MOS transistor NMTr2 are incorporated into the respectivesubsequent-stage basic circuits. In each basic circuit, the MOStransistor NMTR2 has the first terminal thereof connected to the seventhMOS transistor NMT4, or the first terminal of a MOS transistorcorresponding to the seventh MOS transistor NMT4 and a gate terminalthereof connected to an input terminal of an input pulse φIN.

Then, the second terminal of the MOS transistor NMTr2 is connected to afixed power source or to a ground potential which is equal to a voltagewhich becomes a source voltage of the MOS transistor out of voltages ofrespective synchronous pulses φ1, φ2 (the minimum voltage when the MOStransistor is of n-type and the maximum voltage when the MOS transistoris of p-type), or which will be the source voltage of the first orsecond synchronous pulse φ1, φ2 which is not less than the thresholdvoltage value of the fourth MOS transistor.

Further, the transistor NMTr1 has the first terminal thereof connectedto the fourth MOS transistor NMT4 or the first terminal of a MOStransistor corresponding to the fourth MOS transistor NMT4 and a gateterminal thereof connected to the input terminal of the input pulse φIN.

Then, the second terminal of the MOS transistor NMTr2 is connected to afixed power source or to a ground potential which is equal to a voltagewhich becomes a source voltage of the MOS transistor out of voltages ofrespective synchronous pulses φ1, φ2 (the minimum voltage when the MOStransistor is of n-type and the maximum voltage when the MOS transistoris of p-type) or which will be the source voltage of the first or secondsynchronous pulse φ1, φ2 which is not less than the threshold voltagevalue of the fourth MOS transistor.

The dynamic ratioless shift register having such a constitution performsa resetting effect such that, when respective nodes are in an unstablecircumstance such as at the timing of supplying electricity, thecircumstance can be improved.

Further, in the above-mentioned respective circuits, the input part isnot limited to the part shown in FIG. 1A and may be constituted as shownin FIG. 5 in which one terminal and the gate terminal of the MOStransistor NMT1 are connected to an input terminal of the input pulseφIN. With this arrangement, substantially the same effect can beobtained.

Embodiment 2

FIG. 6A is a circuit diagram which shows another embodiment of a shiftregister formed in a liquid crystal display device according to thepresent invention. This embodiment is constituted differently from theembodiment 1 in which the OFF level is held by adding the loadcapacitance. That is, this embodiment is constituted such that a circuitis added which changes an input gate of a shift register which is notselected to “L”. That is, as shown in FIG. 6A, first of all, aMOStransistor NMT1 has the first terminal and a gate terminal thereofconnected to an input terminal of an input pulse (PIN thus forming aninputting part.

The MOS transistor NMT1 has the second terminal thereof connected to agate terminal of a MOS transistor NMT4 and the first terminal of a MOStransistor NMT2. Further, the second terminal of the MOS transistor NMT1is connected to the first terminal of a capacitance element CB1. Thesecond terminal of a capacitance element CB2 is connected to the secondterminal of a MOS transistor NNT4 and the first terminal and a gateterminal of a MOS transistor NMT5.

The first terminal of the MOS transistor NMT2 is connected to a gateterminal of a MOS transistor NMT7 and a gate terminal of the MOStransistor NNT2 and the second terminal of a MOS transistor NMT3 areconnected to the second terminal of a MOS transistor NMT10.

The second terminal of the MOS transistor NMT2 is connected to a fixedpower source VSS or a ground potential (VDD) which is equal to avoltage, which becomes a source voltage of the MOSTFT out of thevoltages of the first and second synchronous pulses φ1, φ2, or whichwill be the source voltage of the first or second synchronous pulse φ1,φ2 which is not less than the threshold value voltage of the MOStransistor NMT4.

Further, the second terminal of the MOS transistor NMT3 is connected tothe fixed power source VSS or the ground potential (VDD), which is equalto the voltage which becomes the source voltage of the MOSTFT out of thevoltages of the first and second synchronous pulses φ1, φ2, or which isnot different from the voltage which becomes the source voltage of thefirst or second synchronous pulse φ1, φ2 to an extent that the fixedpower source or the ground potential at least does not exceed athreshold value voltage of the MOS transistor NMT4.

The first terminal of the MOS transistor NMT4 is connected to the inputterminal of the synchronous pulse φ2, while the second terminal of theMOS transistor NNT5 is connected to a gate terminal and a first terminalof a MOS transistor NMT6, and is further connected to the first terminalof the capacitance element CB2.

The second terminal of the capacitance element CB2 is connected to thesecond terminal of a MOS transistor NMT8, the first terminal and thegate terminal of a MOS transistor NMT9 and the first terminal and thegate terminal of the MOS transistor NNT1 thus constituting a firstoutput terminal.

The first terminal of the MOS transistor NMT6 is connected to a gateterminal of a MOS transistor NMT11, while the second terminal of the MOStransistor NMT11 is connected to the fixed power source VSS or to theground potential (VDD), which is equal to the voltage which becomes thesource voltage of the MOSTFT out of the voltages of the first and secondsynchronous pulses φ1, φ2, or which will be the source voltage of thefirst or second synchronous pulse φ1, φ2 which is not less than thethreshold value voltage of the MOS transistor NNT4.

The first terminal of the MOS transistor NMT8 is connected to the inputterminal of the synchronous pulse φ1 and the second terminal of thetenth MOS transistor NMT9, thus constituting a second output terminal.The gate terminal of the MOS transistor NMT6 and the first terminal ofthe MOS transistor NMT7 are connected to the second terminal of otherMOS transistor, which corresponds to the previously-mentioned MOStransistor NMT10 of a circuit of next stage which adopts a constitutionsimilar to that of the above-mentioned circuit.

The manner of operation of the shift register having such a constitutionwill be described hereinafter in conjunction with the timing chart shownin FIG. 6B. When the input pulse φIN is changed such that “L”

“H” at the time t0, the MOS transistor NMT3 is turned ON so that thenode N5 and the ground potential VSS(=GND) are connected so that theoutputs VN5, VSS become VN5=VSS, the MOS transistor NMT2, which usesnode N5 as the gate turns OFF and the node N1 becomes the floatingstate.

At this point of time, the output VN1 of the node N1 simultaneouslybecomes such that VN1=Vφ−Vth due to the diode connection of the MOStransistor NMT1. When the relationship Vφ−Vth>Vth is established, sinceVN1=Vφ−Vth, the MOS transistor NMT7 also turns ON so that the node N8and the ground potential VSS(=GND) are connected, whereby therelationship VN8=VSS is established. Further, the MOS transistor NMT6,which uses the node N5 as the gate, turns OFF, and the node N3 becomesthe floating state.

At this point of time; among the MOS transistors NMT5 which have thedrains thereof connected to the synchronous pulses φ1, φ2, only thegates of the MOS transistor NNT4 and the MOS transistor NMT7 become thefloating state. When the synchronous pulse φ2 is changed such that “L”

“H” at the time t1, since the MOS transistor NMT4 is in the ON state,the potential of the node N2 rises and the potential VN2 becomesVN2=Vφdue to the bootstrap capacitance CB1 as mentioned previously.

At this point of time, due to the boosting of voltage at the node N1,the output VN1 rises until the voltage v1 becomesVN1=(Vφ−Vth)+Vφ(Cb/(Cb+Cs)). However, the input pulse φIN is in the “H”state and the gate of the MOS transistor NMT2 is set to the relationshipVSS (=GND) so that the forced OFF state is held.

Then, due to the MOS transistor NMT5, which is subjected to the diodeconnection, the output VN3 becomes VN3=Vφ−Vth. Accordingly, the MOStransistor NMT11, which uses the node N3 as the gate becomes the ONstate, so that the node N11 is changed such that “H”

“L”, the MOS transistor NNT15 turns OFF, and the node N6 becomes thefloating state.

At this point of time t2, the synchronous pulse φ1 is changed such that“L”

“H”, while the synchronous pulse φ2 is changed such that “H”

“L”. Although the output VN2 becomes “H”

“L” when the synchronous pulse φ2 is changed such that “H”

“L”, the output VN3 is held at “H”. When the synchronous pulse φ1 ischanged such that “L”

“H”, the output VN4 of the node N4 becomes VN4=Vφ through the MOStransistor NMT8, which is in the ON state.

Accordingly, the MOS transistor NMT16 which uses the node N6 as the gatebecomes the ON state and the node N14 is changed such that “H”

“L” so that the MOS transistor NMT20 becomes the OFF state and the nodeN9 becomes the floating state.

Simultaneously, due to the MOS transistor NMT10, which is subjected tothe diode connection, the output VN5 becomes VN5=Vφ−Vth. Accordingly,the MOS transistor NMT2 which uses the node N5 as the gate becomes theON state so that the node N1 and the ground potential VSS are connectedto each other and the MOS transistor NMT4 is forced OFF, in which thegate of the MOS transistor NMT4 is connected to the ground potentialVSS. Since the MOS transistor NMT10 is subjected to the diodeconnection, even when the output VN4 becomes VN4=“L” thereafter, theoutput VN5 holds the “H” state (previously-mentioned a element beingomitted for the sake of brevity). That is, until the input pulse φINbecomes “H” again, the forced OFF state in which the gate of the MOStransistor NNT4 is connected to the fixed power source VSS is held.

At a point of time t3, the synchronous pulse φ2 is changed such that “L”

“H”, while the synchronous pulse φ1 is changed such that “H”

“L”. Although the output VN4 becomes “H”

“L” when the synchronous pulse φ1 is changed such that “H”

“L”, the output VN6 is held at “H”. When the synchronous pulse φ2 ischanged such that “L”

“H”, the output VN7 of the node N7 becomes VN7=Vφ through the MOStransistor NMT12 which is in the ON state.

Due to the MOS transistor NMT13, which is subjected to the diodeconnection, the output VN9 becomes VN9=Vφ−Vth. Accordingly, the MOStransistor NNT21, which uses the node N9 as the gate, turns ON and thenode N14 is changed such that “H”

“L” so that the MOS transistor NNT25 turns OFF and the node N12 becomesthe floating state.

Simultaneously, due to the MOS transistor NMT14, which is subjected tothe diode connection, the output VN8 becomes VN8=Vφ−Vth. Accordingly,the MOS transistor NMT6, which uses the node N8 as the gate, turns ON sothat the node N3 and the ground potential VSS are connected to eachother and the MOS transistor NNT8 forced OFF in which the gate of theMOS transistor NMT8 is connected to the ground potential VSS. Since theMOS transistor NMT14 is subjected to the diode connection, even when theoutput VN7 becomes VN7=“L” thereafter, the output VN8 holds the “H”state (previously-mentioned a element being omitted for the sake ofbrevity). That is, until the voltage VIN becomes the “H” again, theforced OFF state in which the gate of the MOS transistor NNT4 isconnected to the ground potential VSS is held.

Thereafter, the shift register is operated by sequentially repeating theabove-mentioned operations.

The shift register having the above-mentioned constitution is configuredsuch that, among the MOS transistors which are connected to thesynchronous pulses φ1 and φ2, unnecessary gates are all connected to theground potential VSS. Accordingly, it becomes possible to make the MOStransistor assume the forced OFF state so that the occurrence ofinstability in operation can be obviated.

In the above-mentioned embodiment, the input part is not limited to theconstitution shown in FIG. 6A. That is, as shown in FIG. 8, the inputpart may be constituted such that the first terminal of the MOStransistor NNT1 is connected to the input terminal of the input pulseφIN and the gate terminal of the MOS transistor NNT1 is connected to theinput terminal of the synchronous pulse φ. With this configuration,substantially the same advantageous effects can be obtained.

Embodiment 3

FIG. 7A is a circuit diagram which shows another embodiment of the shiftregister formed on the liquid crystal display device of the presentinvention.

In the drawing, a circuit is constituted such that thin film transistorsNNTR1, NMTR2, NNTR3, . . . which are subjected to the diode connectionusing respective nodes N11, N14, N17, as sources thereof and the inputpulse signal (PIN as drains and gates thereof are connected to thecircuit exemplified in the embodiment 2.

These respective thin film transistors NMTR1, NNTR2, NMTR3, . . .reinforce the “H” level of respective nodes in the floating state whenthe input pulse signal φIN becomes the “H” state, thus making the forcedOFF state of the non-selected input gate more reliable.

Further, an advantageous effect is obtained in that, at the start ofscanning immediately after the supply of electricity, an initializationequal to that of the normal operating state can be performed.

Although the thin film transistors which constitute the shift registerhave been described as n-type transistors in the above-mentionedrespective embodiments, it is needless to say that p-type transistorscan be used as the thin film transistors. This is because, by using theabsolute potential of “H” and “L” levels of respective signals in aninverted manner, the advantageous effects of the present invention canbe obtained substantially in the same manner.

Further, although the thin film transistors are exemplified as MOStransistors whose gate insulation films are made of SiO₂, for example,in the above-mentioned respective embodiments, it is needless to saythat the gate insulation films may be made of SiN, for example.

Embodiment 4

FIG. 11 is a circuit diagram showing another embodiment of aratioless-type dynamic shift register which is used in the displaydevice of the present invention. That is, this embodiment shows afurther improvement of the dynamic shift registers shown in theabove-mentioned respective embodiments. Further, FIG. 12 shows an inputpulse timing chart of the circuit shown in FIG. 11.

Here, to clarify the characterizing portion of the ratioless-typedynamic shift register which is used in the display device of thepresent invention, a circuit diagram which is used for comparison isshown in FIG. 13. Further, FIG. 14 shows an input pulse timing chart ofthe circuit shown in FIG. 13.

In such a circuit, a jumping of the H1 clock is observed at a VSS (GND)level of a node 3 in FIG. 13. FIG. 15A illustrates this phenomenon,wherein an H1 clock after an input signal Hin appears at the VSS (GND)level (lower side of the drawing) of the node 3.

Due to a pulse which enters a node 5 through a diode from a node 4 shownin FIG. 13, a MIS transistor MtrI is turned ON. If this state continuesuntil the next frame time is over (if leakage does not occur at the node5), no problem arises. However, in actual operation as shown in FIG.15D, the leakage of signals occurs at the node 5.

Accordingly, the above-mentioned MIS transistor MtrI turns OFF and,hence, the node 1 becomes the floating state and unstable. The similarphenomenon occurs also at the node 2.

In view of the above, in the ratioless dynamic shift register of thisembodiment, which is used in the present invention, to a MIS transistorMtr2 which is connected to ground levels of respective outputs ofrespective stages of the dynamic shift register, a MIS transistor Mtr3,which is provided separately from the MIS transistor Mtr2, is connectedin parallel.

That is, the MIS transistor MtrI shown in FIG. 13, which drops thepotential level of the node 2 to the ground potential vSS (GND), is,first of all, constituted of the MIS transistor Mtr2 and the MIStransistor Mtr3, which are connected in parallel.

In such a constitution, the MIS transistor Mtr3 has a function similarto that of the MIS transistor Mtr1 shown in FIG. 13, while the MIStransistor Mtr2 has a function of always dropping the node 1 to the VSSlevel, except for a case in which a High signal is supplied to the node1 shown in FIG. 11.

To be more specific, the gate of the MIS transistor Mtr2 is always heldat the High state due to a potential charged in response to an H2 clock.

To avoid a phenomenon in which the charge which is charged to the node 7leaks to the node 6 as a diode inverse current due to the lowering ofthe potential of the node 6 below the ground potential VSS, a MIStransistor Mtr9 is provided.

In connection with the ratioless dynamic shift register having such aconstitution, a step for charging the charge to the node 7 will beexplained.

First of all, since the node 6 constitutes a floating node (the nodewhich is not connected to the power supply), the node 6 is oscillated inresponse to the timing of a clock H2 (see the waveform chart of the node6 shown in FIG. 12).

During the period in which the node 1 is set to “High”, the potential atthe node 7 is dropped to the VSS level and becomes the floating statewhile holding this potential.

Thereafter, when the node 6 is elevated due to the clock H2, the currentflows through the diode, and even when the potential of the node 6 islowered, the charge is held due to the inverse-direction connection ofthe diode (see the waveform chart of the node 7 shown in FIG. 12).

Assuming that the charge held by the node 7 is lost due to a sort ofleakage of current, the node 6 is oscillated in response to the timingof the clock H2 so that the node 7 is charged again immediately.Accordingly, the potential is set such that the potential is not loweredbelow (VSS−(Vth of Mtr8)) with the provision of the transistor Mtr9.

When the potential of the node 6 is set to the ground potential VSS, thepotential held by the node 7 is expressed by an equation ((High ofamplitude of the node 6)−(Vth of the diode)). Further, the amplitude, ofthe node 6 is determined by the capacitance C1 and other floatingcapacitance C0 and is expressed by an equation ((High of the clockH2)×C1/(Ci+CO)).

Further, in the ratioless dynamic shift register shown in FIG. 11, withrespect to the ground levels other than signals of High level in theoutputs of respective stages, means which surely drops the outputs tothe ground levels is constituted of MIS transistors Mtr4, Mtr5, Mtr6,Mtr7 and MtrB.

First of all, the MIS transistors Mtr4 and Mtr5 will be described. Thewaveforms of the node 4 and the node 5 are formed as shown in the timingchart of FIG. 12 in response to the clocks H1, H2, respectively.

The node 4 and the node 5 become the ON state when the clocks H1, H2become High and drop the potential of the node to the gate signal lineto the VSS level thus performing a role to make the node stable.

In this case, when the node 2 is at the High level (when the High levelsignal is outputted to the gate signal line), the MIS transistors Mtr6and Mtr7 are turned ON and the potentials of the node 4 and the node 5are dropped to the VSS level so that the MIS transistors Mtr4 and Mtr5are turned OFF.

The MIS transistor Mtr8 is connected to prevent the potential of thenode 4 from becoming smaller than (VSS−(Vth of Mtr8)). When thepotential of the node 4 is largely lowered from the ground potentialVSS, the amplitude of the clocks H1, H2 does not meet the thresholdvoltage Vth of the MIS transistors Mtr4, Mtr5 (the potential equal to ormore than VSS+Vth being necessary to turn on the MIS transistors Mtr4,Mtr5) and hence, the provision of MIS transistors Mtr8 becomesmeaningless.

Further, as shown in FIG. 11, this embodiment includes a MIS transistorMtr2 which is connected to the ground levels of respective outputs ofrespective stages, and a MIS transistor which is operated with an outputof the front stage and has one end thereof connected to the ground leveland the other end thereof connected to the H2 clock through thecapacitance element C1 and further connected to the gate of the MIStransistor Mtr2. A capacitance C2 is disposed between the other end ofthe MIS transistor Mtr2 and the ground level.

When the potential of the node 1 is dropped to the VSS level due to thenode 3, the node 7 becomes the floating node which is not connected tothe VSS level and, simultaneously, the node 2 is elevated in response tothe Hi clock.

At this point of time, there exists a possibility that the gate (node 7)is elevated due to the capacitance CG between the gate and the drain ofthe MIS transistor Mtr2 so that the node 2 is connected with the groundpotential VSS. To prevent such a phenomenon, the capacitance C2 isprovided.

Accordingly, a boosted amount of potential at the node 7 becomesCG/(CG+C2+other floating capacitance) times so that by increasing thecapacitance C2 compared to CG, the elevated amount of potential becomesa value which can be ignored.

Although the present invention has been explained with respect todynamic ratioless shift registers which are provided for liquid crystaldevices, for example, in the respective embodiments, the presentinvention is not limited to these shift registers and it is needless tosay that the present invention is applicable to dynamic ratioless shiftregisters which are provided for EL display devices, for example.

As has been described heretofore, according to the present invention,the display device which includes the dynamic ratioless shift registerwhich is operated in a stable manner and can expand the degree offreedom of designing can be realized.

1. A display device comprising: a display panel; and a display drivingcircuit including a ratioless dynamic shift register formed on thedisplay panel, the ratioless dynamic shift register including aconnection of a plurality of stages, at least one of the stagesincluding a first transistor and a second transistor, the firsttransistor including a gate electrode, a first electrode and a secondelectrode, wherein a voltage of the gate electrode of the firsttransistor is boosted by a voltage of the first electrode thereofchanging from low level to high level, wherein the second transistorforms a connection between the gate electrode of the first transistorand a ground voltage line when the second transistor is in an on state,and wherein a third transistor holds the second transistor in the onstate until the first transistor is triggered to the on state.
 2. Adisplay device according to claim 1, wherein an output signal from apreceding stage is inputted into the second transistor of a next stage.3. A display device according to claim 1, wherein a first input line forreceiving a first synchronous pulse is connected to the first transistorof a preceding state, and wherein a second input line for receiving asecond synchronous pulse is connected to the first transistor of a nextstage.
 4. A display device comprising: a display panel; and a displaydriving circuit including a ratioless dynamic shift register formed onthe display panel, the ratioless dynamic shift register including: aconnection of a plurality of stages, at least one of the stagesincluding a first transistor and a second transistor, the firsttransistor including a control electrode, an input electrode and anoutput electrode, and being adapted to have a voltage of the controlelectrode boosted by a clock pulse inputted into the input electrodethereof, the second transistor connecting the gate electrode of thefirst transistor and a ground voltage line when the second transistor isin an on state, and being adapted to release restriction of afluctuation of the voltage of the control electrode of the firsttransistor by a start signal, wherein a third transistor holds thesecond transistor in the on state until the first transistor istriggered to the on state by the start signal.
 5. A display deviceaccording to claim 4, wherein an output signal from a preceding stage isinputted into the second transistor of a next stage.
 6. A display deviceaccording to claim 4, wherein a first input line for receiving asynchronous pulse is connected to the first transistor of a precedingstage, and wherein a second input line for receiving a synchronous pulseis connected to the first transistor of a next stage.
 7. A displaydevice comprising: a display panel; and a display driving circuitincluding a ratioless dynamic shift register formed on the displaypanel, the ratioless dynamic shift register including a connection of aplurality of stages, at least one stage including a first transistor, asecond transistor and a third transistor, the first transistor includinga control electrode, an input electrode and an output electrode, whereina clock signal line is connected to the input electrode to input a clocksignal to the input electrode, wherein the voltage of the controlelectrode of the first transistor is boosted when the clock signal ischanging from low voltage to high voltage, wherein the second transistorconnects the control electrode of the first transistor and a fixedvoltage when the second transistor is in an on state, and wherein thethird transistor holds the second transistor in the on state until thefirst transistor is triggered to the on state.
 8. A display deviceaccording to claim 7, wherein an output signal from the output electrodeof the first transistor of a preceding stage is inputted into thecontrol electrode of the first transistor of a next stage as a startsignal.
 9. A display device according to claim 7, wherein the clocksignal includes a first clock signal and second clock signal, wherein afirst clock input line for receiving the first clock signal is connectedto the input electrode of the first transistor of a preceding stage, andwherein a second clock input line for receiving the second clock signalis connected to the input electrode of the first transistor of a nextstage.